IPv6 ULA-Central

This policy is intended to allow the assignment of IPv6 blocks within the so-called 'Centrally Assigned Unique Local IPv6 Unicast Addresses' to organisations or individuals requiring it. These addresses are globally unique and intended for local communications, usually within a site or set of them and are not expected to be routable on the global Internet. Prefix FC00::/7 is already reserved by IANA for ULA (bit 8 determines if locally or centrally assigned, so ULA or ULA-Central).

This policy is intended to allow the assignment of IPv6 blocks within the so-called 'Centrally Assigned Unique Local IPv6 Unicast Addresses' to organisations or individuals requiring it. These addresses are globally unique and intended for local communications, usually within a site or set of them and are not expected to be routable on the global Internet. Prefix FC00::/7 is already reserved by IANA for ULA (bit 8 determines if locally or centrally assigned, so ULA or ULA-Central).

Rationale:

Arguments Supporting the Proposal

In some situations, especially large sites in organisations, which already may have Global Unicast IPv6 blocks, may require an additional block for their internal infrastructure.

This additional block can be used for a number of purposes, such as VPNs, site-to-site communications, avoiding dual/multiple faced DNSs, support for applications which are sensitive to long convergence times (such as VoIP), etc.

The 'Micro-allocations for Internal Infrastructure' document from ARIN (Policy Proposal 2006-2, authored by Jason Schiller et al., describes the need of this kind of additional block for purposes BGP Re-Convergence, Internal Infrastructure Security and why locally assigned ULAs (RFC4193) addresses are not appropriate. Such policy proposal was accepted thru the PDP and it is already part of the ARIN NRPM.

The usage of Global Unicast IPv6 blocks for this type of purposes must be considered as wasteful, especially when there is already an IANA reserved prefix (FC00::/7) for doing so.

Arguments Opposing the Proposal

None foreseen. However, it should be clear that the original scope of ULA-central is for large managed sites and all other cases should use locally assigned ULAs as per RFC 4193. From the same document, it is clearly documented the reasons why this prefix will not be useful as IPv6 PI and will be filtered out in the global Internet.

Acknowledgements

I would like to acknowledge to the authors of the ULA-Central work at IETF, Bob Hinden and Brian Haberman and all those who also contributed to that work.

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